PanoSalado is an open source Flash 10 and Flex based viewer for cubic, equirectangular (spherical), cylindrical and QTVR panoramas. It handles multi-resolution tiled panoramas, and playback of panoramic video in common projections. It supports 2D & 3D hotspots, audio, video, and being extended via XML or directly via Actionscript (AS3) and/or MXML. See PanoSalado's blog, download source and examples from the IVRPA repository and access the API.

PURE Player for Flash is a free Flash 9 based player that supports cylindrical, spherical and cubic panoramas.

SPi-V is a very sophisticated and smooth viewer based on Macromedia Shockwave that handles panoramas completely in graphics card memory (free version with logo).

Syborg Rooms can connect multiple panoramas and enrich the expierence with videos, images and text. Rooms are build with Syborg Architect - an easy graphical interface. It supports iPhone and iPad as well.

Commercial

The Flash Panorama Player is a cross-platform viewer that displays QTVR movies as well as equirectangular (spherical) and cylindrical panoramas. Cube faces and stripes can also be handled. It supports SWF-plugins to extend its functionality (for example to integrate distorted FLV-movies as hotspots).

Pano2VR (formerly Pano2QTVR) creates Flash 9 and Flash 10-compatible SWF files with included spherical viewer. It also creates QuickTime VR content and can output images in a number of different projections including equirect and cubefaces.

KRPano is a Flash 9 & 10 based panorama viewer with a wide range of configuration options. These include different projections such as stereographic, 'little planet', fisheye, Vedutismo, and 'architectural'. It can handle cubefaces, equirects and QTVR .mov files, and it can embed other media including audio and FLV videos into panoramas.

HTML5 based Viewers

Free

Syborg Rooms exports virtual tours in flash and html5. Based on the users device the export shows the supported format.

freepv is a standalone hardware accelerated QTVR viewer as well as a plugin.

Panini is an open source panoramic image viewer and perspective tool for all Qt platforms, including Linux, Windows, OSX. It can display files in many panoramic formats. Your video driver must support OpenGL version 1.5, 2.0 for full functionality. Get Panini at sf.net/projects/pvqt, or build on OS X.

PangeaVR for iPhone and iPod Touch is an app that plays panoramas (max 2048x1024px equirects) using OpenGL. The standard version of PangeaVR is free, the Pro version (which can store panoramas locally for offline viewing) costs $5.99.

PanoBender is a free standalone viewer for JPEG images of equirectangular and cylindrical panoramas. (Windows CE)